The present invention relates generally to the field of manufacturing technology, and more particularly to reliability testing of power package materials.
Printed circuit boards (PCBs) may be exposed to extreme environment (e.g., high temperatures). A conformal coating is a thin polymeric film applied on the surface of PCBs, wherein the conformal coating prevents corrosion, leakage currents, and electric shorting due to condensation. Assembled PCBs (PCBAs) contain embedded electronic components (e.g., capacitors, and resistors) which are typically soldered onto a surface of the PCB. PCB mechanically supports and electrically connects electronic components using conductive tracks, pads, and other features which are etched from copper sheets laminated onto a non-conductive substrate. PCBs may be single sided (e.g., one copper layer), double sided (e.g., two copper layers), or multi-layered (e.g., outer and inner layers).
PCBs are designed via layout software. The designing process takes into account: (i) the schematic capture (i.e., circuit design); (ii) the card dimensions and template based on the required circuitry and properties of the PCB; (iii) the positions of the electronic components and heat sinks to be embedded on the PCB or attached to the PCB; (iv) the layer stacks (e.g., ground and power planes within the PCB); (v) the line impedance matching (i.e., the maximization of electric power transfer/minimization of signal reflection from an electric lead) based on dielectric layer thickness, routing copper thickness, and trace-width; (vi) the placement of electronic components based on thermal and geometric considerations; (vii) the routing of signal traces; and (viii) the generated Gerber files for manufacturing. The manufacturing of PCBAs involves many steps such as: inputting Gerber files into Computer Aided Manufacturing (CAM) software; panelization (e.g., grouping PCBs for manufacturing onto a panel); copper patterning (e.g., subtractive, additive, and semi-additive processes); chemical etching (e.g., removing materials to create an object with the desired shape via etching chemicals); automated optical inspection (e.g., scanning the PCB and comparing the scanned PCB with the digital image deriving from the Gerber files); laminating materials to yield trace layers inside a PCB; drilling holes through a PCB; plating PCBs with solder, tin, or gold over nickel as a resist for etching away the unneeded underlying copper; coating PCBs with solder or some other anti-corrosion coating; applying solder resists on select areas of the PCBs; printing a legend on one or both sides of PCBs; and populating the PCB with electronic components in order to yield the PCBA. Assembly and component defects may occur during the production of PCBAs.